Design of Advanced Digital Heartbeat Monitor using Basic Electronic Components Souvik Sinha, Shankha Mukherjee, Tamal Mukhopadhyay, Subhadeep Pal, Subhadip Mandal Department of Electronics and Communication Engineering Institute of Engineering and Management Kolkata, India
Gautam Ghosh Department of Electronics and Communication Engineering Institute of Engineering and Management(IEM) Kolkata, India
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Abstract - This paper illustrates the design of an efficient, stable, accurate and cheap digital heartbeat monitor which accepts the mechanical heartbeat pulses as input, converts them into the electrical form, amplifies them and provides the necessary output on a 7 segment display following a basic logic algorithm. The reading which is obtained in the seven segments is made error free by using suitable cascading flip flop mechanism. An accurate result is thus obtained.
With the help of this technology, heart beat can be measured in a cost effective way and via further improvements, the reading can be forwarded to the hospital authority.
TABLE I VARIATION OF HEARTBEAT READINGS (BPM) OF PEOPLE OF DIFFERENT AGES
Keywords – Sallen-Key Filter, Sensor, Instrumentation Amplifier, Flip Flop, Seven Segment Display
I.
T
INTRODUCTION
he heart rate is the speed of the heart that is measured in terms of number of contractions per minute generally referred to as beats per minute(bpm). This is generally dependant on the physiological activities of the human body which includes the body’s ability to absorb oxygen and release carbon dioxide. The bpm is largely dependent on age and physical activities and for an average healthy adult, it varies between 60-100 bpm. However, the heart rate of a fatal patient can vary abruptly which may lead to serious medical issues and is a vital reason which it needs to be measured efficiently. Problems in the cardiovascular systems are generally common amongst people who are above the age of 60 and they require quick medical attention for successful treatment.
Athlet e Excelle nt Good Above Averag e Averag e Below Averag e Poor
Age 1825 49-55
26-35
36-45
46-55
56-65
49-54
50-56
50-57
51-56
Abov e 65 50-55
56-61
55-61
57-62
58-63
57-61
55-61
62-65 66-69
62-65 66-70
63-66 67-70
64-67 68-71
62-67 68-71
62-65 66-69
70-73
71-74
71-75
72-76
72-75
70-73
74-81
75-81
76-82
77-83
76-81
74-79
82+
82+
83+
84+
82+60
80+
II.
DESIGN PROCEDURE
Figure 2: Diagram of TCP1000 heartbeat sensor
` Figure 1: Block Diagram of the circuit modelled
The designed circuit can be split into several modules which are explained below:A. Sensor Module The sensor which has been used in the circuit is a TCRT1000 which consists of an Infra Red (IR) diode transmitter and a photodiode receiver as shown in Figure 2. The finger is placed between the sensor and receiver sections. Infra red light is emitted from the IR Diode a part of which is absorbed by the blood inside the veins and the other part is reflected and absorbed by photodiode as an electrical signal. As the amount of blood flowing through the wrist is directly proportional to the voltage drop across the receiving photodiode, the voltage received is directly dependant on the heartbeat rate and be used to work with. The signal which was received can be considered as an equivalent A.C. signal with an amplitude of 4mV and a frequency of 1-1.7 Hz (for an average human adult).
B. Instrumentation Amplifier Since the output of the sensor is very low (4mV approx), amplification of the signal is necessary. To amplify the signal, we have designed instrumentation amplifier using LM 354 chip as shown in Figure 3. An instrumentation amplifier has low DC offset, low drift, low noise, very high open loop gain, very high common mode rejection ratio and very high input impedance. These are mainly used to maintain high stability and provide accuracy. The gain of the instrumentation amplifier is given by Gain (G) = Putting the values of R4=R3=100KΩ, we obtain, Gain (G) = Fixing the value of R1 = 50KΩ, the value of R2 only determines the gain of the amplifier, Gain (G) = When R2 is chosen as 100Ω, we obtain gain to near about 1000. Therefore, the output voltage V0 = G (V2 – V1) With V2 – V1=4mV, we obtain, V0 = 1000(V2-V1) V0 = 4V.
R2 is adjusted to make V0 = 5V
Fcutoff = 2 Hz.
Therefore, the input analog voltage of the pulse which was in the order of millivolts is now converted to the order of considerable Volts so that it can be fed into the input terminals of any digital device filter.
Figure 4: Sallen-Key Filter circuit D.
Figure 3: 3: Circuit Diagram of Instrumentation Amplifier C. Filter The voltage which is obtained from the output terminals of the instrumentation amplifier is enough to proceed with the digital display. However, amplification of the above signal leads to the superimposition of high frequency unwanted noise signals with the baseband signals which must be eliminated in order to proceed for accurate counting of the heartbeat pulses. As mentioned earlier, the human heart for an average adult person contracts 60-100 times per minute, i.e. the frequency of heart beat impulses lie roughly between 1 Hz-1.7 Hz. Therefore, all signals which have frequency above 1.7 Hz are undesirable and must be attenuated from the circuit. For this reason, we use a second order active low pass SallenKey Filter as shown in Figure 4 which provides for a more steeper drop of signals with frequencies greater than the cut off frequency(chosen to be 2 Hz in our case). Putting the values of R1, R2, C1, C2 as C1 =1.125 µF C2 =462.5 nF R1=R2 =10KΩ If we feed use these values of the resistors and capacitors we obtain
Wave Shaper/ADC
The wave shaper module comprises of an ADC converter to convert the low frequency analog signal into a digital pulse so that it can be fed directly into the counter input terminals. We can use a Schmidt trigger circuit with an operational amplifier to this. The output of the Sallen-Key filter is fed into the input of the Schmidt trigger which generates an equivalent square waveform output maintaining the same frequency. E. Pulse generator A monostable multivibrator is used to generate a constant pulse with the following duty cycles. TON = 240 seconds The trigger is turned on for 240 seconds. The purpose of generating the constant pulse is that we desire to measure the total number of beats per minute. This circuit is obtained by using MM74C221. The T ON of multivibrator is set to 4 minutes because the total number of pulses generated at the output of ADC (including AND gate) is considered for 4 minutes duration and then the ultimate number of pulses is divided by 4 using two D Flip Flops cascaded in series to convert the total number of pulses to number of pulses per minute. This is made to improve the accuracy of the system so that if there is any slippage of pulse by the sensor the system will take care of this by considering the number of pulses for a sufficient larger duration (here it is 4 minutes).The output of this monostable multivibrator is fed to one of the input terminals of a two input AND gate while the other input of the AND gate is connected to the output of the low pass filter followed by a Schmitt trigger.
F. Counting and Display Module The counter and display unit comprises of 3 decade counters (for displaying 0 bpm to 999 bpm). Output of each decade counter is connected to a latch which is in turn conncected to a BCD to 7 segment display driver for connection to the seven segment display unit. The input of the clock signal of the first decade counter is the output of the AND gate. III.
WORKING OF PROPOSED HEARTBEAT MONITORING SYSTEM
The working procedure of the above circuit is illustrated in the following steps:-
seconds are obtained. This operation is done to increase the accuracy of our system. G. The output of the D Flip Flop is fed directly to the input terminals of the Decade Counter and counting of the pulses begins. H. The complemented output of the monostable multivibrator is passed to the control inputs of the latch so that when the counting of the pulses in the counter are in process, the latch is turned off. I.
After 240 seconds the monostable multivibrator produces a zero output so the output of the AND gate and the corresponding D Flip Flop is 0 and the counting stops. The complemented output of the latch is now 1 and the latch is activated which passes the output of the DCUs to the driver of 7-segment display.
J.
In this condition, the latch(which is activated) is connected to the 7 segment display so that the total number of pulses counted are displayed.
A. The finger is placed near the sensor which immediately converts the mechanical heartbeat pulse into an electrical A.C. signal B. This analog signal is fed to the input terminals of the instrumentation amplifier so that the signal strength is amplified enough smoothing out of noise (if any )and for further process. C. The signal after getting amplified is passed through a Sallen-Key Filter to eliminate the highest frequency components. D. The corresponding signal after getting amplified, is passed through an analog to digital converter circuit (a Schmidt trigger circuit in our case) which converts the analog wave into a digital wave pulse so that counting of wave pulses becomes easier. E. Now the output of the ADC is fed to the input terminals of an two input AND gate, the other input is connected to the output of a monostable multivibrator. The multivibrator is triggered when the finger is placed over the senser. The output of the monostable multivibrator is designed to to provide a 240 seconds pulse. Therefore the output of the AND gate will be a series of pulses for 240 seconds durations (4 min) corresponding to number of heart beats for 4 minutes F.
The output of the AND gate is fed to the input terminals of 2 D Flip Flops connected in cascade so that the total number of pulses gets divided by 4 and total number of heartbeat pulses available for 240/4=60
TABLE II OVERALL WORKING OF THE CIRCUIT
Monostable Output Counter Latch Display
During 240 seconds of operation 1
After 240 seconds of operation 0
ON OFF OFF
OFF ON ON
IV.
CONCLUSION
The circuit topology so designed calculates the heartbeat signals in an efficient manner by counting the number of beats for four minutes duration then converting it to number of beats for one minute duration to finally display the value of heart beat in bpm. The use of Instrumentation Amplifier and Sallen Key Filter enhances respectively the stability of the sensor and also improves the efficiency and accuracy of the system. The logic which is applied at the display unit caters for the conditional flickering of the heart beat pulses and safely filters the noise
signals prohibiting them from superimposing upon the heartbeat baseband signal. V.
FUTURE SCOPE
The system that we have designed counts the heartbeat pulses using decade counters. Improvements can be made in this regard using a basic 8051 microcontroller instead of the BCD counter. Also the count generated can be transmitted in a wireless medium to individual cellular phones so that doctors can have quick access to a patient’s heart beat count. REFERENCES [1]
[2]
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[4]
[5]
Nisha Singh, Sr.Asst. Prof. Ravi Mishra, Microcontroller Based Wireless Temperature And Heart Beat Read Out, IOSR Journal of Engineering (IOSRJEN), e-ISSN: 2250-3021, p-ISSN: 2278-8719, Vol. 3, Issue 1 (Jan. 2013), ||V5|| PP 01-06 M.M. A. Hashem, Rushdi Shams, Md. Abdul Kader, and Md. Abu Sayed, Design and Development of a Heart Rate Measuring Device using Fingertip, Department of Computer Science and Engineering, Khulna University of Engineering & Technology (KUET), Khulna 9203, Bangladesh, 2010 Mohamed Fezari, Mounir Bousbia-Salah, and Mouldi Bedda, “Microcontroller Based Heart Rate Monitor”, The International Arab Journal of Information Technology, Vol. 5, No. 4, 2008.suited for short distance communication, and the transmission distance is limited only about 10 meters, and then i can be suitable for in- patient monitoring. The system is important to be applied to patient care Bandana Mallick, Ajit Kumar Patro, HEART RATE MONITORING SYSTEM USING FINGER TIP THROUGH ARDUINO AND PROCESSING SOFTWARE. International Journal of Science, egineering and Technology Research (IJSETR), Volume 5, Issue 1, January 2016 Hashem et al, Design and Development of a Heart Rate Measuring Device using Fingertip?, IEEE International Conference on Computer and Communication Engineering (ICCCE), ISBN: 978-14244-6235-3, 2010.
